1. Field of the Invention
The present invention relates to a high-temperature generator for use, for example, in an absorption chiller heater.
2. Description of the Related Art
FIGS. 3 and 4 are schematic illustrations of a conventional high-temperature generator used in an absorption chiller heater for heating an absorption liquid. FIG. 3 is a vertical cross sectional view and FIG. 4 is a horizontal cross sectional view taken along the line A--A of FIG. 3. As shown in FIGS. 3 and 4, the conventional high-temperature generator has a combustion chamber 2 defined in a flue 2a in which a burner 1 is provided at an end thereof.
In the combustion chamber 2, a tube assembly is provided, which includes a bare tube assembly 3 and a finned tube assembly 4 arranged at a downstream of a combustion gas 12 emanating from the burner 1. The bare tube assembly 3 is comprised of bare tubes 31, i.e., heat transfer tubes without fins, extending vertically so as to communicate the upper and lower spaces out of the flue 2a. The bare tubes 31 are arranged in a staggered manner or in a zigzag manner in the gas flow direction for a high efficiency heat exchange with the combustion gas 12. That is, the tubes of the adjacent rows are arranged offset relative to each other in the gas flow direction. The finned tube assembly 4 is comprised of finned tubes 41 extending vertically and arranged in a staggered manner in the gas flow direction. Each finned tube 41 has fins 41a on the outer surface thereof.
The flue 2a for defining the combustion chamber 2 is surrounded by a pipe shell 6. Between the pipe shell 6 and the flue 2a, there is defined a liquid space 5 in which liquid to be heated is introduced. The pipe shell 6 has an inlet 7 in the bottom, an outlet 8 at the upper area of the side wall and the refrigerant vapor outlet 9 at the top. In the upper portion of the liquid space 5, a gas-liquid separation space 10 is defined comprising a baffle 11.
In the high-temperature generator described above, the combustion gas 12 in the combustion chamber 2 exchanges heat with the liquid within the liquid space 5 through the flue 2a. The heat is transferred mainly by radiation and convection to the flue 2a. Then the combustion gas 12 flows to the bare tubes 3 and the finned tubes 4 to exchange heat with the liquid therein. The absorption liquid is heated through the flue 2a, the bare tubes 3 and the finned tubes 4, and is separated into refrigerant vapor and condensed absorbent, which are discharged from the refrigerant vapor outlet 9 and the absorbent outlet 8, respectively.
However, the conventional high-temperature generator has the following disadvantage. Since the bare tubes 31 and the finned tubes 41 are arranged in a staggered manner uniformly, the combustion gas 12 having passed through the bare tube assembly 3 flows to directly hit the finned tubes 41 arranged in a first row of the finned tube assembly 4. This may cause a local overheat of the finned tubes 41 in the first row, which is enhanced because the finned tubes 41 have a large outer surface area due to the fins 41a provided thereon. The local overheat of the outer surface causes a more intensive local overheat of the internal wall of the finned tube 41 compared to that of the bare tube 31. The local overheat of the finned tubes 41 may result in a generation of incondensible gas to lead to the deterioration of the chilling performance as well as to corrosion.